Interbody vertebral prosthetic and orthopedic fusion device with self-deploying anchors

ABSTRACT

A prosthesis includes: a body including a first major surface for engaging an endplate of a first vertebral bone of a spine, a second major surface for engaging an endplate of an adjacent, second vertebral bone of the spine; at least one aperture extending from within the body and opening at the first major surface; at least one anchoring element disposed within the aperture and including a shaft having proximal and distal ends; and a drive mechanism engaging the proximal end of the at least one anchoring element and operating to push the at least one anchoring element out through the at least one aperture and into the first vertebral bone, without rotating the at least one anchoring element about an axis thereof.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication No. 61/612,423, filed Mar. 19, 2012, and U.S. ProvisionalPatent Application No. 61/756,707, filed Jan. 25, 2013, the entiredisclosures of which are hereby incorporated by reference.

BACKGROUND

The present disclosure generally relates to apparatus and methods fortreatment of spinal disorders using an intervertebral prosthesis whichis disposed in an intervertebral space (or cavity) following removal ofa damaged or diseased intervertebral disc. However the varied orthopedicembodiments of this apparatus and the methods used therein constitutethe basic concept of the invention of fusion cages implanted throughoutthe human skeleton.

The bones and connective tissue of an adult human spinal column consistof more than thirty three discrete bones coupled sequentially to oneanother by a tri-joint complex. Each tri-joint complex includes ananterior disc and two posterior facet joints. The anterior space betweenadjacent bones are cushioned by collagen spacers referred to asintervertebral discs. The spine nomenclature of these bones areanatomically categorized as being members of one of fourclassifications: cervical, thoracic, lumbar, or sacral. The cervicalportion of the spine, which comprises the top of the spine, up to thebase of the skull, includes the first seven vertebrae. The intermediatetwelve bones are the thoracic vertebrae, and connect to the lower spinecomprising the five lumbar vertebrae. The base of the spine includes thesacral bones (including the coccyx). The component bones of the cervicalspine are generally smaller than those of the thoracic spine, which arein turn smaller than those of the lumbar region. The sacral regionconnects to the pelvis.

The spinal column is highly complex in that it includes all these bonesand viscoelastic structures coupled to one another, housing andprotecting critical elements of the nervous system having innumerableperipheral nerves and circulatory bodies in close proximity. In spite ofthese conditions, the spine is a highly flexible structure, capable of ahigh degree of curvature and twist in nearly every direction.

Genetic or developmental irregularities, trauma, chronic stress, tumors,and degenerative wear are a few of the factors that can result in spinalpathologies for which surgical intervention may be necessary. A varietyof systems have been disclosed in the art that achieve immobilizationand/or fusion of adjacent bones by implanting artificial assemblies inor on the spinal column. The region of the back that needs to beimmobilized, as well as the individual variations in anatomy, determinesthe appropriate surgical protocol and implantation assembly. The spinesurgical community has accepted intervertebral devices (commonly knownas interbody spacers, and allograft transplants) as part of the state ofthe art and routinely employ such devices in the reconstruction ofcollapsed inter-vertebral disc spaces.

Surgeons insert these intervertebral devices to adjunctively facilitatebone fusion in between and into the contiguous involved vertebrae. Thisfusion creates a new solid bone mass, which acts to hold the spinalsegment at an appropriate biomechanically restored height as well as tostop motion in a segment of the spine in which the patient isexperiencing pain. Items surgically placed in these involved interbodyregions can thus stimulate interbody bone in-growth such that theoperated anterior spinal segments heal into a contiguous bone mass; inother words, a fusion occurs. Further, the surgical community uses suchman-made implants or biological options to provide weight bearingsupport between adjacent vertebral bodies, and thereby correct oralleviate a variety of mechanically related clinical problems. In thisregard, surgeons use intervertebral spinal implants/transplants forsurgical therapy for degenerative disc disease (DDD), discogenic lowback pain, spondylolisthesis, reconstruction following tumor orinfection surgery, and other spine related maladies requiring surgicalintervention.

In many implant designs, a relatively hard or sturdy implant constructis formed from a selected biocompatible material such as metal, ceramic,plastic, or carbon fiber-reinforced polymer. This implant constructoften has a partially open or porous configuration and is coated orpartially filled with a selected bone ingrowth-enhancing substance, suchas harvested bone graft supplied from the patient, human donor allograftbone transplant material supplied by a tissue bank, geneticallycultivated bone growing protein substitutes, and/or otherbiological/biochemical bone extenders. Such devices, when implanted intothe intervertebral space, promote ingrowth of blood supply and growactive and live bone from the adjacent spinal vertebrae to inter-knitwith the implant, thereby eventually immobilizing or fusing the adjacentspinal vertebrae. Such implants also commonly include a patternedexterior surface such as a ribbed or serrated surface, or screw threadgeometry, to achieve enhanced mechanical locking with the adjacentvertebrae during the bone ingrowth/fusion process.

With respect to the failure of the intervertebral disc, the interbodyfusion cage has generated substantial interest because it can beimplanted into the anterior aspect of the spine. Cylindricalintervertebral discal cages generally comprise a tubular metal bodyhaving an external surface threading. They are inserted transverse tothe axis of the spine, into preformed cylindrical holes at the junctionof adjacent vertebral bodies. The cages include holes through which theadjacent bones are to grow. Additional materials, for example autogenousbone graft materials, may be inserted into the hollow interior of thecage to incite or accelerate the growth of the bone into the cage.

Conventional intervertebral discal cages generally comprises a devicewith a geometry that mimics the shape of the intervertebral disc, madeof plastic, carbon fiber, metal, or human tissue, having an upper andlower surface which are designed to interface with well prepared flatvertebral body endplate structures. These cages are designed tointerface transversely to the axis of the spine into completely shelledout disc spaces, the geometry of the cage mirroring the hollowintervertebral disc space. The cages include at least one large grafthole in line with the spinal axis through which the superior andinferior endplates may form an osseous column and fuse. Typically, theseholes are packed with a variety of graft, graft enhancing, bonegenerating, or bone substitute like materials.

Additionally, the spine surgery community has generated severalcommercially available cages with integrated screws that operate asstand-alone support devices (that is, without supplemental support froman additional construct such as an anterior plate and screws, orposteriorly placed transpedicular screws and rods or screws placedthrough the facet joints) interbody fusion devices. These devicesinclude the Stalif™, SynFix™, and the VerteBridge™. The Stalif™ is adevice for the fusion of the lumbar spine. The implant is inserted andfixed via converging screws passing through pre-drilled apertures of thedevice that penetrate into the vertebral bodies. The screws are manuallyplaced into the apertures of the device and are driven using anappropriate tool, such as a surgical screw driver. The Stalif™ isavailable from Centinel Spine, www.centinelspine.com. The SynFix™ isalso a device that is placed in an intervertebral space and fixed viadiverging screws passing through the device and into the vertebralbodies. Again, the screws are manually placed into the apertures of thedevice and are driven using a surgical screw driver. The SynFix™ isavailable from Synthes, Inc., 1302 Wrights Lane East, West Chester, Pa.19380 (www.synthes.com). The VerteBridge™ is a device for the fusion ofthe spine in which anchoring blades are press-driven (using aspecialized tool) through apertures in the device and into therespective vertebral bodies to fix the device in place. The VerteBridge™is available through the LDR Spine (www.ldrholding.com).

All of the above-described devices have an anchor which is secondarilyadded to the initial device. The Stalif™ and SynFix™ devices employscrews while the VerteBridge™ utilizes a blade anchor. Both the Stalif™and SynFix™ devices require the screws to be inserted at trajectoriesthat are difficult to achieve given common human anatomical structures,especially at the spinal disc space levels of L4-L5-S1. Additionally,the proximal end of the screws may protrude anteriorly, causingpotential irritation and erosion to the great and small vessels, andpossibly through innocent misadventure snag ureters and surrounding softtissue as the screw is blindly approximated and then secured into itshome/locked position.

The VerteBridge™ has a pair of blades inserted after the initial deviceis put in place. The blades are supposed to flex enough to curve withinthe device, and to exhibit sufficient strength to cut through bone.These blades, although flexible, need to be able to hold the vertebralbodies in place in all planes of motion under normal physiologic and, toa degree, superphysiologic conditions. In practice, these features maynot always be achieved.

A number of devices have been developed, which employ self-containedanchoring elements that are deployed after the device is placed into theintervertebral space. For example, U.S. Patent Application Pub. No.2006/0241621 (incorporated herein in its entirety) discloses a devicefor joining intervertebral members together using a self-drilling screwapparatus. The screw apparatus includes a shell and first and secondscrew members having tapered ends and threaded bodies that are disposedwithin the shell. A drive mechanism rotationally drives the first andsecond screw members from the shell in precisely co-axial, oppositedirections, which causes the screw members to embed themselves in thevertebral bodies. U.S. Pat. No. 5,800,550 (incorporated herein in itsentirety) discloses a device for joining intervertebral members togetherusing a self-deploying pair of posts. The apparatus includes a body andfirst and second post members that are disposed within the body. A drivemechanism press-drives the first and second posts from the body inprecisely co-axial, opposite directions (longitudinally aligned with thespine), which causes the posts to embed themselves in the vertebralbodies. The problems with these devices include that the co-axial,opposite deployment of the screws/posts is not an ideal configurationfor fixing an intervertebral device. Indeed, such a deployment maypermit slippage of the device during or after deployment because of thenatural stresses applied to the device from the patient's anatomicalspinal structures.

Another approach is disclosed in U.S. 2010/0161057, the entiredisclosure of which is incorporated herein in its entirety. Thatpublication discloses an intervertebral prosthesis that includes a bodyhaving one or more apertures extending transversely therefrom withrespect to the longitudinal axis. Respective anchoring elements disposedwithin the apertures are threaded and deploy in response to a drivingrotational force on a gear. The gear is disposed adjacent to, and inmeshed threaded communication with, the threaded shaft of the anchoringelements such that rotation of the gear causes rotational torque of theanchoring elements. The driving rotational force on the gear causes theanchoring elements to rotate, deploy from the body, and thread into thevertebral bone of the patient's spine.

Despite the advancements in the art, there is nevertheless a need for anew intervertebral device that includes self-contained anchoring membersthat deploy in response to rotational, pulling, or pushing drivingforces.

SUMMARY OF THE INVENTION

Embodiments of the present invention are stand-alone interbody devices,which may be designed in the general style of an anterior lumbarinterbody fusion (ALIF) device, a transforaminal lumbar interbody fusion(TLIF) device, a posterior lumbar interbody fusion (PLIF) device, or afar anterior lateral interbody fusion (FALIF) device. In addition, thesize and/or shape of the basic embodiments disclosed herein may beadapted by the skilled artisan for use in various levels of the spine,namely the cervical spine, the thoracic spine, and the lumbar spine.Thus, while various embodiments herein may be described by way ofexample with respect to the lumbar spine, such disclosures apply withequal weight to the other levels of the spine.

The device includes a body made from any variety of structuralbiomaterial including, but not limited to, any of a number ofbiocompatible implantable polymers, including PEKK, PEKEK,polyetheretherketone (PEEK) being preferred, Titanium, ceramic, etc. Theexternal body surface may have a variety of surface textures, surfacecoatings, and surface geometries, including serrated superior and/orinferior surfaces to provide initial resistance against migration.Additionally, there may be at least one opening extending from thesuperior surface to the inferior surface for the purpose of containing afamily of graft materials, such as autograft, bone morphogenetic protein(BMP), bone marrow aspirate/concentrate, etc.

The body contains at least one anchor therein, which may be deployedfrom the body of the device via a drive mechanism through an associatedaperture. The at least one anchor penetrates the vertebral bone adjacentto the device to secure the device in place.

In accordance with one or more embodiments, a prosthesis includes: abody including a first major surface for engaging an endplate of a firstvertebral bone of a spine, a second major surface for engaging anendplate of an adjacent, second vertebral bone of the spine; at leastone aperture extending from within the body and opening at the firstmajor surface; at least one anchoring element disposed within theaperture and including a shaft having proximal and distal ends; and adrive mechanism engaging the proximal end of the at least one anchoringelement and operating to push the at least one anchoring element outthrough the at least one aperture and into the first vertebral bone,without rotating the at least one anchoring element about an axisdefined the length of the anchoring element itself, i.e., the major axisof the anchoring element.

One of the benefits of the embodiments of the invention is the ease withwhich the devices may be used. There are fewer steps as compared withconventional devices because at least one (and preferably all) of theanchors can be deployed from the body of the device using the same toolfrom inserting the device into the intervertebral space. Furthermore,because the anchors are self-contained, there is no difficult trajectoryneeded to place and tighten screws as with previous devices.

Other aspects, features, advantages, etc. will become apparent to oneskilled in the art when the description of the preferred embodiments ofthe invention herein is taken in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

For the purposes of illustrating the various aspects of the invention,there are shown in the drawings forms that are presently preferred, itbeing understood, however, that the invention is not limited to theprecise arrangements and instrumentalities shown.

FIG. 1A is a perspective view of an intervertebral prosthetic device inaccordance with one or more embodiments of the present invention;

FIG. 1B is a side (lateral) view of the intervertebral device of FIG.1A;

FIG. 1C is an anterior elevational view of the intervertebral device ofFIG. 1A;

FIG. 2 is an illustration of the intervertebral device of FIG. 1 in use;

FIG. 3A is a partial see-through lateral-perspective view of theintervertebral prosthetic device of FIG. 1A showing an example of theinner construction of the device;

FIG. 3B is a lateral elevational view of the intervertebral prostheticdevice of FIG. 3A showing a schematic view of deployed anchors anddirections of deployment;

FIG. 3C is a schematic, 3-D orthogonal coordinate view of directionalcomponents of the anchoring elements of the intervertebral prostheticdevice of FIG. 3A;

FIG. 4 is a posterior-perspective view of an intervertebral prostheticdevice with alternative deployment directions and with anchoringelements deployed;

FIG. 5A is a perspective view of certain of drive mechanism componentsin cooperation with anchoring elements shown outside the body of theintervertebral prosthetic device;

FIG. 5B is a perspective view of a translator element of the drivemechanism of FIG. 5A;

FIG. 5C is a perspective view of an anchoring element shown withoutengagement to the drive mechanism of FIG. 5A;

FIG. 6, illustrates an alternative drive mechanism to deploy theanchoring elements from the device; and

FIG. 7 is a perspective view of an intervertebral prosthetic device withalternative characteristics (with anchoring elements deployed).

DETAILS OF THE EMBODIMENTS OF THE INVENTION

Reference is now made to FIGS. 1A, 1B, and 1C, which illustrate anintervertebral prosthetic device 100 in accordance with one or moreembodiments of the present invention. FIG. 1A illustrates a perspectiveview of the intervertebral device 100. FIG. 1B is a lateral (side) viewwith the left of the drawing being in the front (anterior) direction andthe right of the drawing being in the rear (posterior) direction. FIG.1C is an anterior elevational view of the intervertebral device 100.

The body of the device may be made from any bio-compatible material,such as any of a number of biocompatible implantable polymers, includingPEKK, PEKEK, polyetheretherketone (PEEK) being preferred, titanium,ceramic, etc.

With further reference to FIG. 2, which shows the device 100 in use, thedevice 100 generally includes a body (or housing) that is sized andshaped to fit in the intervertebral space between adjacent vertebralbones 10, 20 of the human spine. It is understood that the size andshape of the device 100 may be adapted to fit in an intervertebral spaceat any level of the spine, such as the cervical spine, thoracic spine,or lumbar spine. The intervertebral device 100 as illustrated in thisexample is designed to be a stand-alone device (e.g., requiring noseparate anchoring devices), which is inserted into the intervertebralspace from an anterior direction. This embodiment is in the general formof an ALIF device, although as will be appreciated from the descriptionherein, the device may be adapted to operate as a TLIF device, faranterior lateral interbody device, PLIF device, used in any level of thespine. In these latter cases, the device may be introduced into theintervertebral space from a direction other than anterior.

The body includes first and second spaced apart major surfaces 102, 104and at least one sidewall 106, 108 extending therebetween. In theembodiment of an ALIF, the sidewalls 106, 108 may be directed in theanterior and posterior direction, respectively. Given the generalgeometry of the body of the device 100, the sidewalls may also includesidewalls, or portions, directed generally in the lateral (medial)directions. The first major surface 102 operates to engage an endplateof the first vertebral bone 10 of the spine, and the second majorsurface 104 operates to engage an endplate of the adjacent, secondvertebral bone 20 of the spine. As best seen in FIGS. 1B and 2, thefirst and second major surfaces 102, 104 define a longitudinal axis Loextending substantially normal to said surfaces and either coaxial with,or generally parallel to, the longitudinal direction of the spine. Withreference to FIGS. 1B and 1C, it is understood that the longitudinalaxis Lo is not precisely normal to the first and second major surfaces102, 104 as there is a slight narrowing height (taper) to the body fromthe sidewall 106 to the sidewall 108. This taper is designed toaccommodate the natural anatomic relationships between the adjacentvertebral bones 10, 20, thereby maintaining the normal lordodiccurvature of the spine.

The surgery involved with implanting the device 100 involves removal ofthe disc material from the intervertebral space, release of thecontracted soft tissues around the disc space, and some degree ofdistraction or pulling apart of the adjacent vertebrae 10, 20 in anattempt to mechanically restore disc space height, realign theanatomical axis of the spine, and indirectly decompress the nerve rootsexiting the spine posteriorly at the particular level. After the surgeonremoves the disc material, a clean aperture (space) is achieved in whichto place the device 100. The surgeon may use a tool to simultaneouslygrasp the body of the device 100, place it at the mouth of theintervertebral space, and apply force so that the device 100 achievesits final placement.

In order to facilitate desirable mechanical interface between theendplates of the respective vertebral bones 10, 20 and the device 100,one or both of the first and second major surfaces 102, 104 of the bodyinclude a bone engagement feature, such as at least one of serrations,protrusions, valleys, spikes, knurling, keels, etc. (not shown).Additionally or alternatively, the intervertebral prosthesis 100 mayinclude one or more apertures 110 extending between and through at leastone of the first and second major surfaces 102, 104 of the body thatoperate to permit dense osseous growth between the body of theprosthesis 100 and the one or more vertebral bones 10, 20.

As illustrated in FIG. 2, once the surgeon has manipulated the device100 into its proper orientation within the intervertebral space, one ormore anchoring elements 120A, 120B are deployed from within the body andengage one or more of the vertebral bones 10, 20. Notably, and as willbe discussed in more detail below, the one or more anchoring elements120A, 120B are pushed out of the body and into the first vertebral bone,without rotating any of the anchoring elements about a major axisthereof, defined by the length of the anchoring element itself. Forexample, the deployment of the one or more anchoring elements 120A, 120Bis not accomplished by threading the anchoring element into thevertebral bones 10, 20. As will also be described in more detail herein,the anchoring elements 120A, 120B deploy from the body into thevertebral bones 10, 20 in directions transverse to the longitudinal axisLo of the body and the spine.

Reference is now made to FIGS. 1A, 1B, 1C, and 3A, where FIG. 3A is apartial see-through lateral-perspective view of the intervertebralprosthetic device of FIG. 1A showing an example of the innerconstruction of the device. The body of the device includes at least afirst aperture 122A extending from within the body, transversely withrespect to the longitudinal axis Lo, and opening at the first majorsurface 102. Preferably, there is a plurality of apertures, with foursuch apertures 122A, 122B, 122C, 122D being preferred.

A first anchoring element 120A is disposed within the first aperture122A in a manner in which deployment of the anchoring element 120Aresults in a trajectory out of the body and into the given vertebralbone in a direction transverse to the longitudinal axis Lo of the bodyand the spine. Preferably, there is a respective anchoring element 120A,120B, 120C, 120D disposed within each of the apertures 122A, 122B, 122C,122D in a manner in which deployment of each anchoring element 120results in a respective trajectory out of the body transverse to thelongitudinal axis Lo of the body and the spine.

Preferably, each anchoring element 120A, 120B, 120C, 120D is in the formof a shaft having a proximal end and a distal end 124A. Each anchoringelement 120 may also include a sharp point at the distal end 124A tofacilitate penetration into the vertebral body in response to a pushingforce at the proximal end.

Although shown in FIG. 3A with a square cross-section, each anchoringelement 120 may have any suitable shape, such as one of: (i) smooth,concentric ringed partially or fully, ribbed, barbed, of multi-lateralcross-section, of quadrilateral cross-section, of trilateralcross-section, of curvilinear cross-section, and of circularcross-section. The associated apertures 122 may be characterized bysmooth walls that permit the anchoring elements 120 to slide andtranslate therethrough during deployment. Although the cross-section ofthe apertures 122 may be of any suitable shape that permits suchsliding, a complementary shape to the cross-section of the anchoringelements 120 is desirable. The concentric ring shaped is the preferredembodiment due to its substantial holding power and back out strength.

Notably, the shaft of each anchoring element 120 is arced along itslength. The arc better facilitates translation and penetration of theanchoring element 120 into the vertebral bone during deployment.Depending on the exigencies of the application, some or all of theanchoring elements 120 may have arced or straight shafts. When arced, itis preferred that the radius of curvature is between 3 mm to about 30mm, with about 10-15 mm being preferred, and about 12 mm being mostpreferred for use in the lumbar spine. The measurement of the radius ofcurvature is from a fulcrum to a farthest (outside) edge of the anchor120.

As noted above, one or more of the apertures 122A, 122B, 122C, 122Dextend within the body transversely with respect to the longitudinalaxis Lo, and each opens at one or the other of the first and secondmajor surfaces 102, 104. In this sense the apertures may be consideredas channels extending through the body in order to guide the anchors 120to their destination and to ensure a proper deployment direction foreach anchor 120. When a given anchor 120 is straight, then theassociated aperture/channel 122 is also preferably straight. When agiven anchor 120 is arced, then the associated aperture/channel 122 isalso preferably arced. When arced, the radius of curvature of theaperture/channel 122 may be any suitable magnitude that permits thesliding and guiding function; however, a complementary radius ofcurvature (which need not be exactly the same) as compared to the radiusof curvature of the associated anchoring element 120 is desirable.

With reference to FIG. 3B, the respective trajectories Lt of theanchoring elements 120 is of importance to achieving desirable fixationof the device 100 within the intervertebral space and avoidance of latermigration during use. In this regard, the size, shape, and orientationof the first aperture 122A, and thus the direction of deployment Lt1 ofthe first anchoring element 120A therefrom, is transverse to thelongitudinal axis Lo of the body. In general, when an anchoring element120 i is straight, then the direction of deployment may be considered tobe along the straight longitudinal axis of the anchor shaft. When theanchoring element 120 i is arced, then there are some options fordefining the direction of deployment.

First, even though the anchoring element 120 i is arced and may deploythrough an arc, for purposes of simplicity, the deployment direction Ltiis nevertheless defined in terms of straight component vectors in a 2Dor 3D coordinate system. Second, the direction of deployment Lti isdefined as a straight composite vector of the component vectors inassociation with the corresponding arced anchoring element 120 i. Oneoption for defining such association is to assume that the straightcomposite vector starts at one point along the arced anchoring element120 i and passes through at least one other point along the anchoringelement 120 i. For example, the composite vector may start at theproximal end of the anchoring element 120 i and passes through anotherpoint, such as the tip of the anchoring element 120 i. Alternatively,the composite vector may start somewhere intermediate along theanchoring element 120 i and pass through the tip of the anchoringelement 120 i. Another example is to use two points, neither of whichare at the proximal or distal extremes of the anchoring element 120 i.In a further alternative, the defined association may not assume thatthe straight composite vector passes through more than one point alongthe anchoring element 120 i, but rather is tangential to a single pointalong the arced anchoring element 120 i.

For purposes of the example illustrated, it is assumed that the straightcomposite vector representing the first direction of deployment Lt1starts at or near the proximal end of the first anchoring element 120Aand passes through an intermediate point. The first deployment directionLt1 includes a first substantial directional component La in an anteriordirection of the body (toward the sidewall 106). The deploymentdirection Lt1 also includes a second substantial directional componentLp parallel to the longitudinal axis Lo of the spine. These componentsof trajectory, Lt=La+Lp, in the anterior and longitudinal directionscharacterize a significant difference with certain prior art techniques,where the deployment is fully in the longitudinal direction of thespine. In a further difference with certain prior art techniques, theanchoring element(s) 120 is/are pushed out of the body and into thevertebral bone, without rotating the anchoring element(s) 120 about anaxis thereof. For example, the deployment of the anchoring element(s)120 is not accomplished by threading the anchoring element(s) 120 intothe vertebral bones 10, 20. Further, the deployment of the anchoringelement(s) 120 is not accomplished by mere rotation thereof about ahinged end. Indeed, as will be discussed further later herein, the endsof the anchoring element(s) 120 that remain within the intervertebralprosthesis 100 during deployment, actually move translationally duringdeployment.

The size, shape, and orientation of the second aperture 122B, and thusthe direction Lt2 of deployment of the second anchoring element 120Btherefrom, is also transverse to the longitudinal axis Lo of the body.More particularly, the deployment direction Lt2 includes a firstsubstantial directional component La in an anterior direction and secondsubstantial directional component −Lp parallel to the longitudinal axisLo of the body and opposite to the second substantial directionalcomponent Lp of the deployment direction Lt1 of the first anchoringelement 120A.

Although not shown in detail in FIG. 3B, similar characteristics andcomparisons may be made to the deployments directions Lt3 and Lt4 of thethird and fourth anchoring elements 120C, 120D.

Reference is now made to FIG. 3C, which is a schematic 3-D view ofdirectional components of deployments directions Lt3, Lt4 of the thirdand fourth anchoring elements 120C, 120D of the intervertebralprosthetic device of FIG. 3A. The third deployment direction Lt3 of thethird anchoring element 120C includes: (i) a first substantialdirectional component in one of an anterior and posterior direction ofthe body (in this example La); (ii) a second substantial directionalcomponent Lp parallel to the longitudinal axis Lo of the body; and (iii)a third substantial directional component L1 in a lateral direction withrespect to the anterior-posterior direction of the body.

Similarly, the fourth deployment direction Lt4 of the fourth anchoringelement 120D includes: (i) a first substantial directional component inone of an anterior and posterior direction of the body (again La in thisexample); (ii) a second substantial directional component Lp parallel tothe longitudinal axis of the body (but opposite of the Lp of the thirddeployment direction Lt3); and (iii) a third substantial directionalcomponent L1 in a lateral direction with respect to theanterior-posterior direction of the body (which is parallel with thethird substantial directional component L1 of the third deploymentdirection Lt3).

With reference to FIGS. 1C, 3A and 3B, in one or more embodiments thedeployment directions Lt1 and Lt2 may also include lateral componentsL1. Notably, the lateral component L1 (which has been referred to as thethird substantial directional component in the examples above) of eachof the deployment directions Lt1 and Lt2 are in the same direction, butare opposite to the lateral components L1 of the deployment directionsLt3 and Lt4. More generally, at least two of the first, second, andthird substantial directional components of either of the third orfourth deployment directions Lt3, Lt4 will be substantially opposite tothe respective first, second, and third substantial directionalcomponents of at least one of the first and second deployment directionsLt1, Lt2 and vise verse.

With reference to FIGS. 1C and 3A, it is noted that the above-describedrelationships of the vector components of the respective deploymentdirections Lt1, Lt2, Lt3, Lt4 reveal an interesting characteristic ofthe collection of deployments. In particular, in some embodiments, thecollection of deployments is characterized by: (i) a point of originwhere all of the actual paths of the deployment (whether arced orstraight) intersect, and (ii) an expansion radially away from the pointof origin. The characteristics of the radial expansion include that therespective paths do not all lay in the same plane.

Generally, the first and second anchoring elements 120A, 120B deploydivergently to one another at an arced angle of greater than about 40°.Similarly, the third and fourth anchoring elements 120C, 120D alsodeploy divergently to one another at an arced angle of greater thanabout 40°.

The anchoring characteristics of the device 100 within theintervertebral space may be adjusted by adding or removing any number ofindividual anchoring elements 120. Indeed as discussed above, as thesize and/or shape of the basic device 100 may be adapted for use in thecervical spine, the thoracic spine, and/or the lumbar spine, so too maythe number of individual anchoring elements 120 be adjusted. Forexample, a lesser number of anchoring elements 120 might be desirable inthe cervical spine than in the thoracic spine and/or the lumbar spine.In addition, the particular deployment directions of the individualanchoring elements 120 may be adjusted in order to best suit theparticular physical bone geometries found in the various levels of thespine.

In one or more embodiments, such as the device 100 of FIGS. 1A-3B, afirst pair of anchoring elements 120A, 120B may be disposed at onelateral side of the body, and a second pair of anchoring elements 120C,120D (of similar construction) may be disposed at another oppositelateral side of the body. In this embodiment, each of the anchoringelements 120 exhibits a deployment trajectory having a substantialcomponent in the anterior direction La (opposite to the posteriordirection).

The above examples disclose a device in which the third lateralcomponent L1 of the directional components of Lt1, Lt2, Lt3, Lt4 are alldirected outwardly. It is noted, however, that one or all of the lateralcomponents L1 may be directed medially by suitable redirection of theassociated aperture.

Reference is now made to FIG. 4, which is a posterior-perspective viewof an intervertebral prosthetic device 100A with alternative deploymentcharacteristics as compared with the intervertebral prosthetic device100. In this view of the intervertebral prosthetic device 100A, theanchoring elements are in a deployed state. The anchoringcharacteristics of the device 100A include first and second pairs ofanchoring elements 120A, 120B and 120C, 120D disposed at oppositelateral sides of the body. In a notable difference with the device 100,each of the anchoring elements 120 of the intervertebral prostheticdevice 100A exhibits a deployment trajectory having a substantialcomponent in the posterior direction (i.e., in the −La direction). Thisis essentially opposite to the deployment of the anchoring elements 120in the device 100.

Reference is now made to FIGS. 5A, 5B, and 5C, which illustrateadditional details of the intervertebral prosthetic device 100 (or100A). FIG. 5A is a perspective view of the main components of a drivemechanism 200, shown in cooperation with four anchoring elements 120.The perspective view shown in FIG. 5A is from an opposite lateral pointof view with comparison to the visible components of the drive mechanism200 shown in FIG. 3A.

At the core, the drive mechanism 200 engages the proximal end of one ormore (preferably all) of the anchoring elements 120 and operates to pushthe anchoring elements 120 out through the respective apertures 122 andinto the vertebral bones. This is accomplished without rotating any ofthe anchoring elements 120 along a longitudinal axis thereof. Notably,when a plurality of anchoring elements 120 are employed, the drivemechanism 200 preferably deploys all of the anchoring elements 120simultaneously, at the same rate and via substantially the sametranslational force.

The drive mechanism 200 includes a drive shaft 202 having a head 204 ata proximal end and a threaded shaft 206 extending therefrom. Thelongitudinal extension of the drive shaft 202 defines a longitudinalaxis thereof. The drive mechanism 200 also includes a translator element210, which engages each of the proximal ends of the one or moreanchoring elements 120. As best seen in FIG. 5B, the translator element210 includes a threaded bore 212 that is in threaded engagement with thethreaded shaft 206 of the drive shaft 202. The translator element 210also includes at least one, and preferably an equal number of couplingelements 214 as there are anchoring elements 120. Each coupling element214 is in engagement with, captivates, but permits articulation of theproximal end of a respective one of the anchoring elements 120. Withreference to FIGS. 5B and 5C, each of the coupling elements 214 includesa socket 216 and the proximal end of each anchoring element 120 includesa ball 126. The ball 126 may be offset from the terminus of theanchoring element 120 by way of a relatively short shaft 128. The ball126 is captive within the socket 216 such that the translator 210 is inengagement with, and permits articulation of, the proximal end of theanchoring element 120 during movement along the longitudinal axis of thedrive shaft 202. It is noted that such articulation may include anynumber of degrees of movement; however, in accordance with at least oneembodiment, the articulation permits movement of the proximal end (andthe distal end for that matter) of the anchoring element 120 in morethan one (and preferably many) axes of rotation as one would expect froma ball-and socket arrangement as compared with a hinge arrangement(which permits movement about a single axis of rotation).

The drive shaft 202 is oriented in an anterior-to-posterior directionwithin the body of the device 100 (or 100A), with at least the head 204thereof accessible external to the body such that a rotational force maybe applied to the head 204 by an operator of the device. In theembodiment of FIG. 3A, the drive shaft 202 is oriented in ananterior-to-posterior direction within the body of the device 100 suchthat the head 204 is accessible at the anterior side of the device 100.In the embodiment of FIG. 4, the drive shaft 202 is oriented in ananterior-to-posterior direction within the body of the device 100A suchthat the head 204 is also accessible at the anterior side of the device100. The major difference then in the orientation of the drivingmechanism 200 within the respective devices 100 and 100A is that theanchoring elements 120 of the former engage and extend away from oneside of the translator element 210 within the body, while those of thelatter engage and extend away from an opposite side of the translatorelement 210 within the body.

Irrespective of which device orientation is employed, the drive shaft202 is fixed in the direction of the longitudinal axis thereof, butrotatable, within the body in response to a rotational force applied tothe head 204. In order to stabilize the orientation of the drive shaft202 within the body, a bearing 220 may be employed at a distal end ofthe shaft 206, opposite to the head 204. The rotation of the drive shaft202 cause a corresponding rotation of the threaded shaft 206 within thethreaded bore 212 of the translator device 210. Such rotation causes thetranslator device 210 to move translationally along the longitudinalaxis of the drive shaft 202 and push the anchoring element(s) 120 outthrough the respective aperture(s) 122 and into the vertebral bone. Thecooperation between the drive shaft 202 and the translator element 210produces a tremendous amount of translational (pushing) force, which issufficient to drive the anchoring element(s) 120 out through therespective aperture(s) 122 and into the vertebral bone without requiringthreading (rotation) of the anchoring elements 120 into the bone.Notably, the translator device 210 causes the proximal ends of theanchoring element(s) 120 to move translationally parallel to thelongitudinal axis of the drive shaft 202. In this sense, deployment isnot accomplished by mere rotation of the anchoring element(s) 120 aboutstationary proximal ends thereof, but rather through pushing,translational movement of the proximal ends of the anchoring element(s)120.

Reference is now made to FIG. 6, which illustrates an alternative device100B having a different drive mechanism to push, pull, or twist theanchoring elements 120 through the respective apertures 122. In thisembodiment, the drive mechanism includes some components disposed withinthe body of the device 100B and one or more external elements. Inparticular, the device 100B includes a translator element 210A, whichengages each of the proximal ends of the one or more anchoring elements120. The translator element 210A may substantially similar to thetranslator element 210 discussed above, and includes a bore therethroughwhich may be non-threaded. The drive mechanism, however, does notinclude the drive shaft 202. Instead, an external shaft element 250 isemployed to enter an aperture 112 of the body and engage the bore of thetranslator element 210A.

In particular, the shaft element 250 includes an extension (or rod) 252that is manipulated by an operator and a distal end 254, which includesan engagement feature. The engagement feature exhibits a releasableconnection to the translator element 210A (such as to the bore) andpermits the operator to push, pull, or twist the anchoring elements 120through the respective apertures 122. In the illustrated embodiment, theshaft 252 is hollow along its length and includes a fluted distal end254 (which may include an optional tapered undercut). The flutes permitthe distal end 254 to flex and press into and through the bore of thetranslator element 210A. Once the distal end 254 is in place, a rod 256is inserted into the proximal end of the shaft 252 (not shown) and isslid all the way to the distal end 254, proximate to the flutes. Thepresence of the rod 256 prevents re-flexing of the flutes and preventsthe tapered undercut from pulling back through the bore of thetranslator element 210A. At this point, the operator may push, pulland/or twist the translator element 210A to achieve desirable movementof the anchoring elements 120.

In the example in which the device 100B shown in FIG. 6 is an ALIF, thetranslator element 210A is movable such that movement thereof along alongitudinal axis in an anterior-posterior direction, pushes or pullsthe at least one anchoring element out through the at least one apertureand into the first vertebral bone, without rotating the at least oneanchoring element about a major axis thereof. In an alternative examplein which the device may be adapted for far anterior lateral insertion,the translator element 210A is movable such that movement thereof alonga longitudinal axis in first and second opposing lateral directions,pushes or pulls the at least one anchoring element out through the atleast one aperture and into the first vertebral bone, without rotatingthe at least one anchoring element about a major axis thereof.

When the operator has completed the deployment of the anchoring elements120, he/she may withdraw the rod 256 at least as far as needed to permitthe flexing of the flutes, and then withdraw the distal end 254 of theshaft element 250 from the bore of the translator element 210A. Thoseskilled in the art will appreciate that there are many other ways toachieve the releasable connection between the shaft element 250 and thetranslator element 210A. For example, the bore of the translator 210Amay be threaded and the distal end 254 of the shaft element 250 may bethreaded to achieve the desirable connectivity.

Reference is now made to FIG. 7, which illustrates an alternative device100C having an alternative drive mechanism to push the anchoringelements 120 through the respective apertures 122. By way of example,the embodiment of FIG. 7 may be particularly suited for far anteriorlateral interbody fusion, owing to the more rectangular shape ascompared with the other devices 100, 100A, 100B. Thus, with reference toFIG. 2, the device 100C may be implanted from a first lateral direction,or a second opposing lateral direction (into or out of the page).

In this embodiment, the drive mechanism includes substantially the samecomponents disposed within the body of the devices 100, 100A, or 100B(see, also FIG. 5A) with some modification. In particular, the device100C includes at least two translator elements 210A, 201B, each havingthe aforementioned threaded bore 212 for threaded engagement with thethreaded shaft 206 of the drive shaft 202. Each of the translatorelements 210A, 201B is coupled to a respective at least one anchoringelement 120 (for a total of four anchoring elements by way of example).The threaded shaft 206 includes first and second portions, the firstportion being threaded in a first direction, and the second portionbeing threaded in a second direction, opposite to the first direction.The first translator element 210A is in threaded engagement with thefirst portion of the threaded shaft 206, while second translator element210B is in threaded engagement with the second portion of the threadedshaft 206.

Deployment of the respective sets of at least one anchoring element 120is accomplished in a manner similar to one or more of the approachesdiscussed above. For example, the rotational force applied to the shaft202 causes the respective first and second threaded portions of thethreaded shaft 206 to rotate (in the direction of the rotational force).Given that each of the first and second threaded portions of thethreaded shaft 206 are threaded in opposing direction, the rotation ofthe shaft 202 causes the respective translator elements 210A, 210B tomove along the longitudinal direction of the shaft 202 in oppositedirections. In the illustrated embodiment, simultaneous deployment ofthe anchoring elements 120 takes place as the respective translatorelements 210A, 210B move away from one another. In an alternativeembodiment, each anchoring element 120 may be disposed on an oppositeside of the respective translator element 210 (with correspondingchanges in the orientation of the respective aperture 122) such thatdeployment of the of the anchoring elements 120 takes place as therespective translator elements 210A, 210B move toward one another.

It is noted that any of the devices 100, 100A, 100B, 100C discussedabove may include one or more of the particular features of each device(where conflicts would not occur) in order to achieve the resultantfunctionality of such feature as would be readily apparent to theskilled artisan. Indeed, for example the device 100C shows the anchoringelements 120 all in the same general plane (i.e., a laterally extendingplane with respect to the geometry of the body of the device). However,modifications to achieve additional variation in the deploymenttrajectories of the anchoring elements 120 may be achieved by takingcertain of the structure and function from other embodiments, and viceversa. Alternatively, or additionally, the deployment of the respectiveanchoring elements 120 may be achieved using the instrument 250 of FIG.6, assuming that the shaft 202 is not employed.

Although the invention herein has been described with reference toparticular embodiments, it is to be understood that these embodimentsare merely illustrative of the principles and applications of thepresent invention. It is therefore to be understood that numerousmodifications may be made to the illustrative embodiments and that otherarrangements may be devised without departing from the spirit and scopeof the present invention as defined by the appended claims.

The invention claimed is:
 1. An intervertebral prosthesis, comprising: abody including first and second spaced apart major surfaces and at leastone sidewall extending therebetween, the first major surface forengaging an endplate of a first vertebral bone of a spine, and thesecond major surface for engaging an endplate of an adjacent, secondvertebral bone of the spine, and the first and second major surfacesdefining a longitudinal axis extending substantially normal to saidsurfaces; at least three apertures extending from within the body andeach aperture opening at one of the first and second major surfaces; arespective anchoring element disposed within each aperture and includinga shaft having proximal and distal ends; and a drive mechanism engagingthe proximal end of each anchoring element and operating to push theanchoring elements out through the respective apertures and into thefirst vertebral bone or the second vertebral bone, without rotating anyanchoring element about a major axis thereof, the drive mechanismhaving: a head at a proximal end of a single threaded shaft extendingtherefrom, thereby defining a longitudinal axis thereof; and atranslator element having: (i) a threaded bore in threaded engagementwith the threaded shaft of the drive shaft, (ii) at least one couplingelement in engagement with, and permitting articulation of, the proximalend of at least one anchoring element, wherein the drive shaft is fixedin a direction of the longitudinal axis thereof, but rotatable, withinthe body, such that a rotation force on the drive shaft causes thetranslator to: (i) move along the longitudinal axis of the drive shaft,(ii) translate each of the proximal ends of the respective anchoringelements parallel to the longitudinal axis of the drive shaft, and (iii)push the respective anchoring elements out through the respectiveapertures such that each anchoring element pierces into one of the firstand second vertebral bones, without rotating any anchoring element aboutthe major axis thereof.
 2. The intervertebral prosthesis of claim 1,wherein at least one aperture and at least one anchoring element areoriented such that the at least one anchoring element deploys outthrough the at least one aperture and into the first vertebral bone in adirection transverse to the longitudinal axis of the body.
 3. Theintervertebral prosthesis of claim 2, wherein the direction transverseto the longitudinal axis of the body includes a first substantialdirectional component in one of: (i) an anterior direction of the spine;and (ii) a posterior direction of the spine.
 4. The intervertebralprosthesis of claim 3, wherein the direction transverse to thelongitudinal axis of the body includes a second substantial directionalcomponent parallel to the longitudinal axis of the spine.
 5. Theintervertebral prosthesis of claim 1, wherein at least one anchoringelement includes a sharp point at the distal end thereof.
 6. Theintervertebral prosthesis of claim 1, wherein the shaft of at least oneanchoring element is arced.
 7. The intervertebral prosthesis of claim 6,wherein the arced shaft of the at least one anchoring element has aradius of curvature that is one of: (i) between about 3 mm to about 30mm, (ii) between about 10 mm to about 15 mm, and (iii) about 12 mm. 8.The intervertebral prosthesis of claim 1, wherein the shaft of at leastone anchoring element is one of: (i) smooth, ribbed, barbed, ofmulti-lateral cross-section, of quadrilateral cross-section, oftrilateral cross-section, of curvilinear cross-section, and of circularcross-section.
 9. The intervertebral prosthesis of claim 1, wherein: theat least one coupling element of the translator includes a socket; theproximal end of the at least one anchoring element includes a ball; andthe ball is captive within the socket such that the translator is inengagement with, and permits articulation of, the proximal end of the atleast one anchoring element during movement along the longitudinal axisof the drive shaft.
 10. The intervertebral prosthesis of claim 1,further comprising: a further translator element having: (i) a threadedbore in threaded engagement with the threaded shaft of the drive shaft,(ii) at least one coupling element in engagement with, and permittingarticulation of, the proximal end of at least one anchoring element. 11.The intervertebral prosthesis of claim 10, wherein: the threaded shaftincludes: (i) a first threaded portion which is threaded in a firstdirection, and (ii) a second threaded portion which is threaded in asecond direction, opposite to the first direction; the threaded bore ofthe translator element is in threaded engagement with the first portionof the threaded shaft of the drive shaft; the threaded bore of thefurther translator element is in threaded engagement with the secondportion of the threaded shaft of the drive shaft; and the rotation forceon the drive shaft simultaneously causes: (i) the translator element tomove along the longitudinal axis of the drive shaft in a firstdirection, and (ii) the further translator element to move along thelongitudinal axis of the drive shaft in a second direction, opposite tothe first direction, thereby pushing the at least one anchoring elementand the at least one further anchoring element out through therespective apertures without rotating the anchoring elements about themajor axes thereof.
 12. The intervertebral prosthesis of claim 1,wherein the drive shaft is oriented in an anterior-to-posteriordirection within the body, with at least the head thereof accessibleexternal to the body such that the rotational force may be applied tothe head by an operator of the device.
 13. The intervertebral prosthesisof claim 1, wherein the drive shaft is oriented in a lateral directionwithin the body, with at least the head thereof accessible external tothe body such that the rotational force may be applied to the head by anoperator of the device.
 14. The intervertebral prosthesis of claim 1wherein the translator element is movable such that movement thereofoccurs along a longitudinal axis in one of: (i) an anterior-posteriordirection, and (ii) first and second lateral directions.
 15. Theintervertebral prosthesis of claim 1, wherein each of the anchoringelements is in sliding cooperation with a respective one of theapertures, wherein the anchoring elements are engaged at respectiveproximal ends thereof with the drive mechanism, which operates to pushthe anchoring elements out through the respective apertures and into thefirst and second vertebral bones, without rotating any of the anchoringelements about respective major axes thereof.
 16. The intervertebralprosthesis of claim 15, wherein: the drive mechanism operates to deployeach of the anchoring elements from the body into one or the other ofthe first and second vertebral bones, and each in a direction transverseto: (i) the longitudinal axis of the body, (ii) the spine, and (iii) toone another.
 17. The intervertebral prosthesis of claim 15, wherein: afirst deployment direction of a first of the anchoring elementsincludes: (i) a first substantial directional component in one of ananterior and posterior direction of the body; and (ii) a secondsubstantial directional component parallel to the longitudinal axis ofthe body; and a second deployment direction of a second of the anchoringelements includes: (i) a first substantial directional component in oneof an anterior and posterior direction of the body; and (ii) a secondsubstantial directional component parallel to the longitudinal axis ofthe body and opposite to the second substantial directional component ofthe first deployment direction of the first anchoring element.
 18. Theintervertebral prosthesis of claim 17, wherein: the first deploymentdirection of the first anchoring element further includes: (iii) a thirdsubstantial directional component in a lateral direction with respect tothe anterior-posterior direction of the body; and the second deploymentdirection of the second anchoring element further includes: (iii) athird substantial directional component in a lateral direction withrespect to the anterior-posterior direction of the body and parallel tothe third substantial directional component of the first deploymentdirection of the first anchoring element.
 19. The intervertebralprosthesis of claim 18, wherein: a third deployment direction of a thirdof the anchoring elements includes: (i) a first substantial directionalcomponent in one of an anterior and posterior direction of the body;(ii) a second substantial directional component parallel to thelongitudinal axis of the body; and (iii) a third substantial directionalcomponent in a lateral direction with respect to the anterior-posteriordirection of the body; and at least two of the first, second, and thirdsubstantial directional components of the third deployment direction aresubstantially opposite to the respective first, second, and thirdsubstantial directional components of at least one of the first andsecond deployment directions.
 20. The intervertebral prosthesis of claim19, wherein: a fourth deployment direction of a fourth of the anchoringelements includes: (i) a first substantial directional component in oneof an anterior and posterior direction of the body; (ii) a secondsubstantial directional component parallel to the longitudinal axis ofthe body; and (iii) a third substantial directional component in alateral direction with respect to the anterior-posterior direction ofthe body; and at least two of the first, second, and third substantialdirectional components of the fourth deployment direction aresubstantially opposite to the respective first, second, and thirdsubstantial directional components of at least one of the first, second,and third deployment directions.
 21. The intervertebral prosthesis ofclaim 15, wherein at least one of: a first deployment direction of afirst of the anchoring elements includes: (i) a first substantialdirectional component in one of a first lateral direction of the bodyand a second, opposing, lateral direction of the body; and (ii) a secondsubstantial directional component parallel to the longitudinal axis ofthe body; a second deployment direction of a second of the anchoringelements includes: (i) a first substantial directional component in oneof the first lateral direction of the body and the second, opposing,lateral direction of the body; and (ii) a second substantial directionalcomponent parallel to the longitudinal axis of the body and opposite tothe second substantial directional component of the first deploymentdirection of the first anchoring element.
 22. The intervertebralprosthesis of claim 21, wherein: a third deployment direction of a thirdof the anchoring elements includes: (i) a first substantial directionalcomponent in one of the first lateral direction of the body and thesecond, opposing, lateral direction of the body; and (ii) a secondsubstantial directional component parallel to the longitudinal axis ofthe body; and at least one of the first and second substantialdirectional components of the third deployment direction issubstantially opposite to the respective first and second substantialdirectional components of at least one of the first and seconddeployment directions.
 23. The intervertebral prosthesis of claim 22,wherein: a fourth deployment direction of a fourth of the anchoringelements includes: (i) a first substantial directional component in oneof the first lateral direction of the body and the second, opposing,lateral direction of the body; and (ii) a second substantial directionalcomponent parallel to the longitudinal axis of the body; and at leastone of the first and second substantial directional components of thefourth deployment direction is substantially opposite to the respectivefirst and second substantial directional components of at least two ofthe first, second, and third deployment directions.
 24. Theintervertebral prosthesis of claim 1, further comprising a boneengagement feature disposed on at least one of the first and secondmajor surfaces of the body, wherein the bone engagement feature includesat least one of serrations, protrusions, valleys, spikes, knurling, andkeels.
 25. The intervertebral prosthesis of claim 1, further comprisingat least one aperture extending between and through at least one of thefirst and second major surfaces of the body that operates to permit bonegrowth between the body of the prosthesis and one or more vertebralbones.